1. Field of the Invention
The present invention relates to a vane or an element sliding against a rotor of a rotary compressor, and more specifically to a zirconia vane preferably applicable in the atmosphere of alternative fluorocarbons used as coolants.
2. Description of the Prior Art
Chlorofluorocarbons (CFCs), which belong to the group of fluorocarbons, have heretofore been used as coolants and refrigerants in refrigerators, freezers, or the like and a representative example of CFCs is CFC12. These CFCs contain chlorine in their molecules, which effectively prevents cohesion and seizure of sliding members against a sliding surface of a compressor. Since CFCs used as the coolants also function as effective lubricants, various metals, such as cast iron, have heretofore been sufficiently used for sliding members of compressors.
Recently, the destruction of ozone in the stratosphere due to chlorine has become a very serious problem and the regulations of the chlorine-containing CFCs represented by CFC12 have been made more rigorous. Therefore, hydrofluorocarbons (HFCs) containing no chlorine in their molecules have been increasingly used as alternative fluorocarbons (hereinafter, referred to as "alternative fleon") substituting for CFCs and, especially, HFC134a or the like are greatly expected.
The HFCs and other alternative coolants containing no chlorine are, however, not expected to have lubricating functions like conventional CFCs and may cause cohesion or seizure of sliding members composed of metals. Development of novel material for sliding members having excellent sliding properties and effectively preventing cohesion and seizure has highly been strongly demanded, especially in compressors using the no chlorine-containing HFCs or other alternative coolants. Appropriate substitutes for conventional metal rotors and vanes are urgently required in rotary compressors having severer sliding conditions, such as high sliding speed and pressure on the sliding surface as compared with the reciprocating type.
As an attempt to substitute the conventional metal material, it has been proposed to prepare a rotor and vane of a rotary compressor from a ceramic material, as disclosed in Japanese Utility Model Laid-Open No. 61-152787. The ceramic materials are expected to improve the abrasion resistance and reduce the weight of the sliding members. Another example disclosed in Japanese Patent Laid-Open No. 5-71484 gives a ZrO.sub.2 vane partially stabilized with Y.sub.2 O.sub.3 According to the invention of this patent, partially stabilized ZrO.sub.2 has a coefficient of thermal expansion, which is substantially similar to those of iron-based materials as counterpart sliding members. No gap between the sliding members efficiently prevents a leakage of the coolant and a drop in compression capacity (see the last line, first column through line 6, second column, page 2 in the specification).
Although attempts have heretofore made to prepare sliding members of rotary compressors from ceramic materials as set forth above, any improvement in the sliding properties, which has recently been demanded, cannot be expected when the conventional partially stabilized ZrO.sub.2 sintered body is used in the atmosphere of alternative fleon coolants like HFCs containing no chlorine, and, thus, it is difficult to prevent cohesion or seizure.